Stress-ribbon bridge construction

How bridges get built · Cable-supported and arch bridges · Stress-ribbon bridge construction

Also called: stressed ribbon bridge, stress ribbon, catenary deck bridge, Spannbandbrücke

How it is done

Build the abutments and anchor blocks first, on drilled shafts, ground anchors or rock anchors sized for the full horizontal tendon force, plus intermediate supports with saddles for multi-span ribbons.
Install the bearing tendons or cables between the abutments over the saddles on low-friction pads, and tension them to the computed erection sag.
Hang precast deck segments (often about 3 m long) on the bearing tendons with a crane at one abutment and pull them along the tendons into position with a winch until the span is filled.
Adjust the profile by tendon force, then cast the saddles over intermediate supports and the joints between segments, using forms hung from the segments.
Thread and stress the prestressing tendons so the whole ribbon stays in compression under live load and temperature, and grout the ducts.
Measure deflections and natural frequencies against the design, and fit dampers if pedestrian-induced vibration is predicted.
Install handrails, surfacing and drainage, and survey the final profile.

Key numbers

Spanabout 30–110 m per span; multi-span ribbons to about 300 m overall (Lake Hodges, 3 × 108.6 m)
Sagabout span/50 to span/80 (Lake Hodges about 1/77), limited by the allowable walking gradient
Deck thicknessabout 250–450 mm (Lake Hodges segments 0.41 m deep)
Precast segmentsabout 1.5–3 m long
Horizontal forcetens of MN per abutment (Lake Hodges up to about 53 MN)
Pedestrian comfortvertical frequencies of about 1.6–2.4 Hz need a walking-excitation check

Where it fits

Footbridges and pipeline bridges of about 30–110 m per span, single or multi-span, over valleys, rivers and reservoirs; sites with rock or competent ground at the abutments; sensitive sites where nothing may be built below, since segments are erected from the abutments.

Where it does not

Weak ground that cannot take the horizontal force economically, decks that must be level or have steep approaches (sag limits the walking gradient), heavy or fast road traffic, single spans so long that the sag would breach gradient limits.

Choosing it

Choose it over a cable-stayed or suspension footbridge where both ends can take large horizontal forces and a shallow sag is acceptable: it needs no towers or stays and little maintenance.
Prefer a suspension or cable-stayed footbridge for spans beyond about 100–150 m, or where the deck must be level.
Prefer an arch-supported stress ribbon or a self-anchored form where the soil cannot take the horizontal force.
Avoid it for heavy or fast road traffic; the few road stress ribbons are short and low-speed (Leonel Viera).

Plant, pace and money

PlantDrilling rigs for shafts or ground anchors, bearing tendon installation and stressing equipment, a crane at the abutment, winches to slide segments, precast yard, grouting plant.

ProductivitySeveral segments placed per day once the bearing tendons are in; a 100 m span erected in a few weeks after the abutments, which take most of the time.

CostIndicative: USD 3,000–8,000 per m² of deck; the abutment anchorages are a large share of the cost.

Risks and controls

What goes wrong

Underestimated horizontal force or anchor creep changing the sag, pedestrian-induced vertical and lateral vibration, cracking at saddles from local bending, corrosion of bearing tendons if grouting is poor, temperature changes altering sag and stresses.

Quality assurance

Proof and acceptance tests of anchors, tendon force records during erection, sag survey at a reference temperature, grout quality control, dynamic testing (frequency and damping) before opening.

Origins

Ulrich Finsterwalder proposed the concept in the late 1950s; the Leonel Viera Bridge at Punta del Este, Uruguay (1965) is credited as the first built, and Jiří Stráský developed the precast-segment method in Czechoslovakia from the 1980s, bringing it to the US with the Sacramento River Trail Bridge (1990).

Examples

Leonel Viera Bridge (Uruguay, 1965), Sacramento River Trail Bridge (Redding, 1990, 127 m), Lake Hodges Bridge (San Diego, 2009, three spans of 108.6 m), and the Czech footbridges designed by Jiří Stráský.

Case studies

Leonel Viera Bridge, Punta del EsteUruguay · 1965Undulating road bridge at La Barra, credited as the first stress-ribbon bridge; a twin was added beside it in 1999.

Sacramento River Trail Bridge, ReddingUSA · 1990127 m single-span precast stress ribbon, the first in the US, designed with Jiří Stráský.

Lake Hodges Bicycle Pedestrian Bridge, San DiegoUSA · 2009Three spans of 108.6 m (303 m overall), the longest stress-ribbon bridge; segments 0.41 m deep and 3.05 m long; horizontal force of up to about 53 MN taken by 2.7 m drilled shafts at one end and rock anchors at the other.